Not much is known about the Squad's past apart from being a gang of thieves and mercenaries working for money. One day they are tasked with raiding Dr. Eggman's base in Mystic Jungle and selling off his tech for money. Eggman (who just discovered the Phantom Ruby), accidentally triggers it, causing it to summon an army of Badnik replicas. With this newfound power, he attempts to defend his base from Jackal Squad to no avail, eventually their leader manages to reach Eggman and goes to deal the final blow, but then comes into contact with the Ruby which causes him to hallucinate a ruined world where he rules as an overlord. Seeing the potential in him, Eggman offers him and his squad to join him as one of the leaders of the Eggman Army. Although the rest of the Jackals were against this offer, The leader accepts.
Sonic Forces: Episode Shadow
Eggman becomes so obsessed with studying the Phantom Ruby and it's power that he becomes negligible to create more Badniks to defend his base. Because of this, Eggman hires the rest of Jackal Squad to protect his base while he does his studies. This attracts the attention of Team Dark, who send Shadow the Hedgehog to raid Eggmans base. When he begins to approach the Bases perimeters, He is attacked by most of the Jackal Squad except for their leader, who Shadow ploughs through killing them in the process. Enraged at Shadow for his squad's death, the Leader attacks Shadow. Shadow effortlessly defeats him and tells him he never wants to see his face again before teleporting away. After his defeat and he realises his fear of Shadow, his inferiority complex is triggered causing him to go insane.
With the tests completed, Eggman gives the Phantom Ruby to the now sole Jackal, granting him ultimate power. The Jackal then dons a mask to hide his face and assumes the identity of Infinite, as we know him today.